1. Field of the Invention
The invention generally relates to digital video multimedia. In particular, the invention relates to audio processing of digital video multimedia.
2. Description of the Related Art
People watch videos for a variety of purposes. For example, videos can be used for entertainment, for education, for communication, and the like. Consumer video can be derived from analog sources, such as videotapes, and from digital sources, such as digital versatile discs (DVDs), video compact discs (VCDs), hard disks, computer networks, direct broadcast satellite (DBS), digital cable, and the like.
Often, one of the constraints placed on the viewing of video is time. For example, a user may desire to view a prerecorded video clip within a time period that is shorter than the run time of the video. Examples include during the duration of a flight, during a class period, during a lunch break, before the beginning of a live program, and the like. In another example, the device that is used to view the video may be battery powered and may not have enough battery life to display the entire video clip at its normal run time without speeding up the presentation of the video clip. In another example, a user who is learning a language may desire to slow down the rate at which words are spoken in a video.
As a result, it is desirable to provide the ability to adjust the speed of a video clip. A video clip typically includes both visual information and audio information, which are synchronized together. The adjusting of the speed of the visual information is relatively simple. Simple techniques, such as increasing or decreasing the frame rate, i.e., the rate at which visual images are displayed, or deleting or repeating images to effectively change the frame rate, can suffice adjusting the speed of visual information. By contrast, a mere change in rate for audio samples is undesirable. When audio samples are merely sped up or slowed down by changing the frame rate or changing the sampling rate, the corresponding pitch of the audio also changes. For example, when a playback rate of audio is merely increased, the familiar effect of vocals is sometimes referred to as “chipmunking.” In another example, the mere deletion or the mere duplication of audio samples can result in undesirable clicks, pops and other audible artifacts.